Lecture-Sea Ice Importance Importance Winter Winter Melt Period Melt Period Freeze-Back Freeze-Back Spatial Distribution Spatial Distribution Summary Summary Importance 2 to 6 m of ice cover between two materials (ocean and air) of greatly different geophysical properties 2 to 6 m of ice cover between two materials (ocean and air) of greatly different geophysical properties The ocean-ice-atmosphere plays an important role in the polar climate, and such an interaction has implications at the local, regional and global scales The ocean-ice-atmosphere plays an important role in the polar climate, and such an interaction has implications at the local, regional and global scales Ice Cover, February and Aug. 2001, and elevation and bathometry Continued It dominates the marine environment for 9 to 12 months depending on the particular geographical location It dominates the marine environment for 9 to 12 months depending on the particular geographical location Characteristics of the ice (surface roughness, lifting force (due to changing water levels), bearing capacity and pressure must be considered) Characteristics of the ice (surface roughness, lifting force (due to changing water levels), bearing capacity and pressure must be considered) Continued Important for marine installations (such as piers or drilling platforms), vessels, or other scientific or industrial activities that may require the use of a sea-covered area as a road, bridge or aircraft landing strip Important for marine installations (such as piers or drilling platforms), vessels, or other scientific or industrial activities that may require the use of a sea-covered area as a road, bridge or aircraft landing strip Prudoe Bay North Pole Importance to Marine Animals Pingo-Polar Bear Pass, Early August 2006 Seasonality of Snow Covered Sea Ice Winter Winter Min. lasts from Nov. to MayMin. lasts from Nov. to May First year ice types cover a range of thicknesses from >0.3 to 0.3 to < 2 m. Typically, first year ice consists of a snow layer covering a primary layer of frazil ice overlying columnar crystals.Typically, first year ice consists of a snow layer covering a primary layer of frazil ice overlying columnar crystals. Total snow cover throughout the winter season reaching accum. of between 0.05 and >1.0 mTotal snow cover throughout the winter season reaching accum. of between 0.05 and >1.0 m Grease Ice Pack Ice First year ice flow Fast Ice Continued The frazil layer consists of randomly oriented crystals and the columnar crystals are more vertically oriented. The frazil layer consists of randomly oriented crystals and the columnar crystals are more vertically oriented. Ice density-uniform- about 920 to 960 kg/m 3. Ice density-uniform- about 920 to 960 kg/m 3. Liquid brine is interspersed throughout the ice as brine-drainage channels and brine inclusions (pockets) in between the crystal network Liquid brine is interspersed throughout the ice as brine-drainage channels and brine inclusions (pockets) in between the crystal network Continued Average length and radius of these inclusions are 3 to 5 mm and mm respectively. Average length and radius of these inclusions are 3 to 5 mm and mm respectively. Multi-year Ice Generally has an uneven surface which has undergone re- crystallization during the previous summer melt period. Generally has an uneven surface which has undergone re- crystallization during the previous summer melt period. The surface consists of an array of preferential melt areas (melt ponds) and desalinated low porous hummocks surrounding the melt ponds. The surface consists of an array of preferential melt areas (melt ponds) and desalinated low porous hummocks surrounding the melt ponds. Multi-year Ice Continued The upper layer of re-crystallized ice (in the hummocks) has widely varying densities typically around 700 kg/m 3. The upper layer of re-crystallized ice (in the hummocks) has widely varying densities typically around 700 kg/m 3. This layer then merges into an intermediary layer of slightly higher density which in turn merges into a more solid layer with densities.about kg/m 3 This layer then merges into an intermediary layer of slightly higher density which in turn merges into a more solid layer with densities.about kg/m 3 Continued The salinity of both hummocks and melt ponds < than first year ice due to brine drainage the previous year. The salinity of both hummocks and melt ponds < than first year ice due to brine drainage the previous year. Early Melt Transition period -warming of the snowpack.and ending when have moisture present in the snowpack and the snowpack is undergoing metamorphism.-changes in snow properties (density, grain size, ). Transition period -warming of the snowpack.and ending when have moisture present in the snowpack and the snowpack is undergoing metamorphism.-changes in snow properties (density, grain size, ). Changes in snowcover create albedo differences between multi-year ice and first year ice Changes in snowcover create albedo differences between multi-year ice and first year ice Continued Snowcover is quickly removed from hummocks but remains longer over the melt ponds Snowcover is quickly removed from hummocks but remains longer over the melt ponds Multi-year Ice < First Year Ice Multi-year Ice < First Year Ice (5-15 %)(5-15 %) Melt Onset Free water is present in snow Free water is present in snow Ice surface is becoming damp Ice surface is becoming damp Salinities rapidly from the surface.surface salinities are heterogeneous Salinities rapidly from the surface.surface salinities are heterogeneous Advanced Melt Water in saturated snow begins to drain Water in saturated snow begins to drain Ice surface undergoes melting Ice surface undergoes melting Diurnal pattern (energy driven) Diurnal pattern (energy driven) Some refreezing at night is possible Some refreezing at night is possible Development of drainage networks Development of drainage networks Seal holes, cracks and leads (fracture openings in the ice)Seal holes, cracks and leads (fracture openings in the ice) The salinity of first year ice decreasesThe salinity of first year ice decreases The ice cover decomposes completely in some areasThe ice cover decomposes completely in some areas Freeze-up New ice begins with the appearance of frazil ice particles in the ice column New ice begins with the appearance of frazil ice particles in the ice column Frazil-consists of thin discs of ice about 1 mm in dia., formed in turbulent water when its temp. falls Frazil-consists of thin discs of ice about 1 mm in dia., formed in turbulent water when its temp. falls Further cooling-consolidation of the surface-frozen frazil-platelette type crystals (mm) Further cooling-consolidation of the surface-frozen frazil-platelette type crystals (mm) Continued freezing leads to secondary ice growth at the base of the sea ice cover (columnar ice crystals) Continued freezing leads to secondary ice growth at the base of the sea ice cover (columnar ice crystals) Pancake Ice Grease Ice Continued Cooling causes brine pocket within frazil layer to be pushed to the surface.frost flowers. Cooling causes brine pocket within frazil layer to be pushed to the surface.frost flowers. Salinities can be considerably higher (~100 ppt). Salinities can be considerably higher (~100 ppt). Salinities here (surf.) can be > than bulk salinity values for the ice Salinities here (surf.) can be > than bulk salinity values for the ice Brine also expelled into the ocean or into the growing young ice mass Brine also expelled into the ocean or into the growing young ice mass Continued Salinity quickly after initial freeze-up Salinity quickly after initial freeze-up After about a week (0.4 m thickness), desalinization decreases more steady rateAfter about a week (0.4 m thickness), desalinization decreases more steady rate Overall surface and bottom salinities are >Overall surface and bottom salinities are > than middle of ice sheet (5 to 15 ppt) Ice Formation Ice formation in sea water is a process requiring heat loss from the water surface Ice formation in sea water is a process requiring heat loss from the water surface It involves vertical convection to a certain depth defined by the salinity.reverse to the formation of cumulus clouds It involves vertical convection to a certain depth defined by the salinity.reverse to the formation of cumulus clouds Rate of cooling.affected by initial water temp., density stratification of the water and atmospheric factors: wind, temp, cloudiness and K and L* Rate of cooling.affected by initial water temp., density stratification of the water and atmospheric factors: wind, temp, cloudiness and K and L* After Ice Forms Situation changes abruptly Situation changes abruptly Heat loss heat conduction Heat loss heat conduction SnowSnow iceice Ice remains weak and rather flexible until it reaches the 15 to 30 cm range Ice remains weak and rather flexible until it reaches the 15 to 30 cm range At this stage, have a temp. gradient of about -1.6 Deg. C/m -this results in hardening of the surface At this stage, have a temp. gradient of about -1.6 Deg. C/m -this results in hardening of the surface Continued Crystals which form in sea water are pure ice and the salts remain in the water Crystals which form in sea water are pure ice and the salts remain in the water As crystals increase, brine is trapped in gaps between crystals As crystals increase, brine is trapped in gaps between crystals Also columnar growthvertical crystals drainage channels for the brine pockets easily develop between them Also columnar growthvertical crystals drainage channels for the brine pockets easily develop between them In old ice -the downward migration of brine-freshening of the floes and in strength In old ice -the downward migration of brine-freshening of the floes and in strength Break-up Process As K in spring-first melting occurs in the snow cover and puddles of meltwater may form within the snow layer itself. As K in spring-first melting occurs in the snow cover and puddles of meltwater may form within the snow layer itself. As vol. of water grows.impt. centres for further melting, snow has high , but water has a low . VERY EFFECTIVE ABSORPTION As vol. of water grows.impt. centres for further melting, snow has high , but water has a low . VERY EFFECTIVE ABSORPTION Continued Once puddles have formed they begin to melt their way into the ice by this energy absorption and will eventually penetrate to the base of the floe and become thaw holes Once puddles have formed they begin to melt their way into the ice by this energy absorption and will eventually penetrate to the base of the floe and become thaw holes Break-up of ice layer into floes is the phase of the process which is least understood Break-up of ice layer into floes is the phase of the process which is least understood Continued Consolidation during freeze-back and any thermal cracks which develop during winter have an effect Consolidation during freeze-back and any thermal cracks which develop during winter have an effect But timing and extent of the fracturing is an observed phenomenon rather than a predictable one.except strong winds But timing and extent of the fracturing is an observed phenomenon rather than a predictable one.except strong winds Afterwaves, swells, floe collisions Afterwaves, swells, floe collisions Cracks and Leads Floe Ice First Year Ice Ridge Polar Sea Ice Has pressure ridges and open water areas Has pressure ridges and open water areas Maykut (1978) reported that approx. 1% of the winter arctic ice cover is open water-despite limited spatial coverage.this dominates the large scale turbulent heat flux between ocean and atmosphere Maykut (1978) reported that approx. 1% of the winter arctic ice cover is open water-despite limited spatial coverage.this dominates the large scale turbulent heat flux between ocean and atmosphere Cracks and Leads Polynas Important: Important: BiologicallyBiologically ClimatologicallyClimatologically Ice being formed and moving in and outIce being formed and moving in and out Cracks and leads.DIFFICULT TO MONITORCracks and leads.DIFFICULT TO MONITOR Continued Without the ice lid, the ocean (temperature near 0 Deg. C) is free to give heat to the atmosphere (temp. can be -30 Deg. C). Without the ice lid, the ocean (temperature near 0 Deg. C) is free to give heat to the atmosphere (temp. can be -30 Deg. C). The loss of heat from the ocean results in a cooler and therefore denser, ocean. The loss of heat from the ocean results in a cooler and therefore denser, ocean. The denser ocean waters can then participate in a stronger deep ocean circulation (www.polar.noaa.gov) The denser ocean waters can then participate in a stronger deep ocean circulation (www.polar.noaa.gov) Continued Polynyas have lots of animal and plant life. Polynyas have lots of animal and plant life. Open waters absorb the suns light energy Open waters absorb the suns light energy Phytoplankton in the polynya use this energy to produce a nutrient rich grazing area for zooplankton Phytoplankton in the polynya use this energy to produce a nutrient rich grazing area for zooplankton Feeding on these small areas are whales and fishes that in turn feed seas, walruses and polar bears. Feeding on these small areas are whales and fishes that in turn feed seas, walruses and polar bears. Cunningham Inlet, Somerset Island Polar climate in a Global System Sea ice acts as a thermal regulator through control of the energy exchange between the ocean and the atmosphere Sea ice acts as a thermal regulator through control of the energy exchange between the ocean and the atmosphere Impt.-open areas:Impt.-open areas: Leads Leads Polynas Polynas Continued Strong temp. contrasts between the water and the colder air coming off the ice force strong energy fluxes from the ocean Strong temp. contrasts between the water and the colder air coming off the ice force strong energy fluxes from the ocean Difference.2 orders of Magnitude Difference.2 orders of Magnitude Higher of ice in comparison to open water has important implications for the absorption of solar radiation Higher of ice in comparison to open water has important implications for the absorption of solar radiation Continued - sea surface = 3 to 10% - sea surface = 3 to 10% - snow covered ice = 70 to 90 % - snow covered ice = 70 to 90 % The effect is that the absorbed radiation of water may be an order of magnitude greater than that of snow covered sea ice. The effect is that the absorbed radiation of water may be an order of magnitude greater than that of snow covered sea ice. Mean date of saltwater cleared of ice Mean concen. of ice June 18 Mean concen. of ice July 16 Mean concen. of ice Aug. 13 Mean concen. of ice Sept. 10 Scientists theorize that the gradual reduction in sea ice results from a combination of shifting atmospheric winds that naturally break up ice cover, as well as higher temperatures, which may be linked to the greenhouse effect. Summary Importance Importance Separates ocean-atmosphere, control on local, regional and global climateSeparates ocean-atmosphere, control on local, regional and global climate Engineering aspectsEngineering aspects Seasonality Seasonality WinterWinter First Year First Year Multi-year ice Multi-year ice MeltMelt Early Early Advanced Melt Advanced Melt Freeze-backFreeze-back